The mass the the sample is 4g. The volume of the sample is 2 cm°. What is the density of the sample in g/cm?

Iknow the answer is a but i don't know why

Consider the reaction: n2(g) + o2(g) ? 2no(g) kc = 0.10 at 2000oc starting with initial concentrations of 0.040 mol/l of n2 and 0.040 mol/l of o2, calculate the equilibrium concentration of no in mol/l how would this be done?

What is the mass of 2.00 l of an intravenous glucose solution with a density of 1.15 g/ml?